Synthetic polymers, including poly-ethylene, -styrene, and -propylene, must retain their functionality over widely varying conditions of temperature and pressure fluctuation, flame exposure, etc. They are consequently synthesized to have backbones of only carbon atoms, which makes them resistant to chemical and enzymatic degradation. Introducing heteroatoms into the polymer backbone creates functional groups, such as esters and amines. These groups increase the polyester's susceptibility to hydrolytic cleavage, i.e. degradation, thereby improving the polyester's ability to biodegrade upon disposal. Moreover, polyester polymers are susceptible to hydrolytic cleavage when exposed to chemical or enzymatic treatment
Many polyester polymers, especially when made of aliphatic monomers, e.g. polyhydroxybutyrate and poly(ε-caprolactone), are considered biodegradable (Muller et al., J Biotechnol, 86:87-95 (2001); Abou-Zeid et al., J Biotechnol, 86:113-126 (2001)). But, aliphatic polyesters lack commercially valuable material properties, like durability, because of their low melting temperatures and increased susceptibility to degradation. In contrast, aromatic polyesters, exemplified by polyethylene terephthalate (PET), have desired durability but are in the main considered non-biodegradable or have unacceptably slow biodegradation rates. (See Kint, D. and Munoz-Guerra, S., (1999) Polym Int 48:346-352).
The balance between functionality and biodegradability is an important consideration in achieving cost-effective waste disposal. Disposable single-use items of aliphatic polyesters are environmentally attractive but generally lack acceptable durability, whereas such items of aromatic polyesters have the preferred functionality but are ecologically burdensome.
A partial resolution to this dilemma is the use of aliphatic-aromatic co-polyesters, which have durability and other preferred attributes and are biodegradable as well. However, the use of high aromatic content co-polyesters in disposable single-use items is still not entirely satisfactory because the rate of biodegradation is proportional to the content of aromatic acid in the co-polyester. The problem in optimizing functionality and biodegradability is that increasing aromatic content improves utility but decreases biodegradability (U.S. Pat. No. 6,521,717 to Itoh, H. and German Patent Application DE 19508737 to Witt et al.).
One strategy for increasing susceptibility to hydrolytic cleavage of these co-polyesters is to treat them with hydrolytic enzymes before or after the co-polyesters enter the waste cycle. Numerous enzymes, known in the art, can degrade polymers containing hydrolyzable groups, such as esters, amides, etc.
For example, U.S. Pat. No. 6,255,451 to Koch et al. describes the use of a cutinase from Humicola insolens and lipases from Aspergillus niger, Mucor Miehei (Lipozyme 20,000 L), and Candida antartica (lipase component B) to degrade substrate polymers that are aliphatic polyesters, aromatic polyester amides or partially aromatic polyester urethanes. International App. No. PCT/US04/16349 to Nagarajan, corresponding to U.S. patent application Ser. No. 10/852,403, which are incorporated herein by reference, describe a method to increase the biodegradation rate of aliphatic-aromatic co-polyesters having more than 60 mol percent aromatic acid content by contacting the co-polymer with at least one hydrolytic enzyme. U.S. Pat. No. 6,066,494 to Hsich et al. and U.S. Pat. No. 6,254,645 to Kellis et al. describe the use of lipases or polyesterases to modify polyester fiber to enhance wettability and absorbancy of textiles. U.S. Pat. No. 6,350,607 to Cooney, Jr. discusses the use of enzymes for treatment of macerated food waste products in conjunction with garbage disposal apparatus. U.S. Pat. No. 5,464,766 to Bruno reports waste treatment compositions containing bacteria and enzymes for municipal and yard waste. However, using purified or partially purified enzymes is often expensive. Plus, processes based on enzymatic pretreatment of the co-polymer followed by composting may not be the most efficient process to degrade aliphatic-aromatic co-polyesters having greater than 60 mol percent aromatic acid content because the mixture of endogenous microbes in the composting system may not be optimally adapted to completely mineralize the polymeric waste.
One way to increase the biodegradation rate of high aromatic content co-polyesters is to use a microbial consortium that has been adapted to biodegrade aliphatic-aromatic co-polyesters, especially sulfonated ones, having greater than 60 mol percent aromatic acid content. To biodegrade such co-polyesters, the microbial consortium must be able to cleave the polymer backbone and mineralize the subsequent products formed.
The problem to be solved is the development of an economical method to increase the rate of biodegradation in typical composting conditions of sulfonated aliphatic-aromatic co-polyesters having more than 60 mol percent aromatic acid content relative to the total acid content. This problem has been solved in the invention described herein, which provides a new microbial consortium (SPDC-1) capable of accelerating the biodegradation of sulfonated aliphatic-aromatic co-polyesters having more than 60 mol percent aromatic acid content relative to the total acid content of the polymer. This invention is economical, fosters the use of composting as a workable waste process, can help eliminate the need for source separation of waste, can provide commercially valuable fertilizer-quality compost and can help accelerate the rate of degradation of high aromatic polyesters disposed in landfills.